7i76ED to servo spindle - connection question

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16 Feb 2021 15:57 - 16 Feb 2021 15:59 #199077 by PCW
It does seem like the drive offset function would allow bi-directional
operation from 0-10V.

To make this work in hal you would offset the spindle output by 1/2 way
(this is simple with a pncconf created configuration, you set the
spindle pid components bias pin and the spindle scale to twice
the maximum RPM)
Last edit: 16 Feb 2021 15:59 by PCW.
The following user(s) said Thank You: spumco

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16 Feb 2021 17:52 #199094 by spumco
Thanks PCW. I'll have a go at the offset 0-10v scheme, and if it doesn't work I'll fall back on PWM.

Does the 7i76ED to drive connection arrangement I posted earlier make sense?

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16 Feb 2021 21:19 #199110 by spumco
And another thing...

I'm wondering about the resolution possible with what is effectively a 0-5v range (in both CW/CCW directions).

If I only have 0-5v of range, then the velocity will be incremented in whatever the smallest voltage increment the 7i76 is capable of outputting.

The drive has 12-bit analog input resolution - so about 3rpm resolution given the 0-5v range and 6000rpm top speed.

To achieve +/-3rpm of control in both directions, the 7i76 SPINDLE OUT would need to adjust in increments of ~0.0025v - that seems unrealistic.

What resolution is the SPINDLE OUT capable of? The specifications in the manual are silent on analog output resolution.

If the RPM resolution is going to wind up being very coarse, then I'll certainly want to shift my plans over to PWM command.

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16 Feb 2021 21:25 #199111 by PCW
I think the resolution is 14 bits but the isolation will introduce perhaps 0.5 to 1 % of non-linearity

BUT in normal use there is not much to be gained with highly accurate spindle speed and even a 5% error is of little consequence.

If you needed better accuracy, the encoder feedback could be used

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16 Feb 2021 22:45 #199113 by spumco
Nope, that'll do nicely. I just didn't want to go through setting this up only to have 500rpm minimum increments.

-R

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